Transom repair advice needed

Hi,
Been doing a lot of research on this site and others on the subject of rot repairs to transoms and stringers. I believe I've reached a point where some expert advice on this particular project would be very beneficial.
What started out as a soft sole repair has turned into a transom and stringer rebuild as well. Once I got the sole out, it became pretty clear that the transom had substantial dry rot. After a lot of research, mostly here, I cut the glass out around the inside of the transom plywood and laboriously removed the plywood with a chisel and assorted other tools.
Since the existing I/O mercruiser was pretty well shot (anyone need a core in the Seattle area for free?) I decided to convert the transom to an outboard design. I've marked and cut the outside transom skin for a 20" shaft outboard and once sanding is complete I'll be ready to cut the new transom core from 3/4" marine ply.
The boat is supported on two cradles. One supports the stern, just below the transom. This one has been constructed to hold the stern nice and level. The other supports the keel, just where it starts to curve up towards the bow. A 2x4 was screwed to the gunnels just fore of the transom to provide additonal support while the transom was gutted. Is this adequate, or should there be more support under the keel? The boat seems pretty stable with my 180 lbs. moving around in it.

All this brings us to where we sit today. I believe (but am fully prepared to be corrected) that I am now ready to cut the new transom core. I'm planning to cut a cardboard template of the outside of the transom, to use as a guide in cutting the new core out. The previous transom core did not extend to the sides of the hull, instead stopping about 1" short. Should the new transom core be cut in the same way, or would it be beneficial to have it snug against the hull? The original transom also extended up to the rub rail. Is it necessary for the new outboard oriented transom to extend up that far on the sides, or can I make the whole thing shorter? I'd love to be able to get the whole core out of a single sheet if possible, but I'm more interested in doing this job right than saving a few bucks. Thanks in advance for your input.

 

Attachments seem to have broken, reposting pics:

 

Rebuilding Transom on runabout

As you have wisely retained the glass outside shell of the old boat, it is a perfect template for the plywood that you are about to cut as you suggested. I have done many of these jobs, and they are all still alive and kicking. Cut and fit your plywood sheets, glue with epoxy from the fibreglass transom inwards the required layers untill the thickness required is met. Screw through each layer into the next till the resin sets, then remove the screws.
On the last insert, do not get any epoxy on the face toward the bow if you intend to finish the interior with fibreglass polyester, as poly does not stick to epoxy. If you are just painting the interior, well the epoxy glue can be smoothed out nicely in the corners to save a lot of fairing work. Glass sheave the interior again when finished, using overlaps right into the topsides (after first grinding off any gelcoat back to clear glass laminate). Overlaps are to be staggered, first one at least 1 foot into the topsides, others reaching lesser degrees back to the transom.

Now that you have made your new transom, it is VERY important now to fit the outboard carefully. When drilling holes through your masterpiece, first drill out a pilot hole. Get a nail and bend it, say 1/2" and put it into a drill. Set this spinning inside the pilot hole and it will smash out the plywood from between the glass laminate of the transom inner and outer. Be careful, but it is pretty tough, so no damage to the glass is likely. Resize the nail to suit different hole applications. What you will have greated is a void between the glass layers. Now fill this hole and the void of course with epoxy and glass filler, put some masking tape on the inside when doing this. Allow to set , then drill out the new hole to suit the bolts for the mounting of the motor. Use Sika or other sealant when mounting bolts thru these holes.

What you will have done is to give the bolts a surface to set through that is obviously watertight, has reinforced the hole and also gives the nut, washers etc something to compress onto, instead of simply crushing the transom as most people do.

Have fun.

 

Thanks for the input, it's much appreciated.
Should the new transom core sit snugly against the sides of the hull, or should it have a gap like the old one did? Assuming a 20" mounting height for the outboard would I be foolish to build a 24" high (at the sides) core? The original extended up to the rub rail, which would require another sheet of ply.
Normally I'd just reproduce the piece I tore out, but it looks to me like what I tore out wasn't the factory piece. It had no glass, or even resin protecting the inside surface of the plywood, just a coat of paint. Looks to me like the stringers have been replaced with a similar quality (or lack thereof) of workmanship so I'll be redoing those as well.
If it makes any difference, I plan to add knee braces glassed between the new transom and new stringers, along with a splash well.

Thank you,
Ryan (MotorHead)

 

The transom core can fit snugly against the corners. When we install bulkheads, they are set off the topsides (we use foam about 1/2" thick), but this is to prevent hard spots on the topsides, and possible warping of the topsides when viewed along them. The hard edge of the ply in the transom area is quite OK as it is a reinforced corner anyhow, and gluing it intimately all around is only a good thing.
The transom is brought up to the top of the corner Ryan and the cut out to suit the motor is lower in the middle. This reinforces massivly the structure of the whole back of the boat. Drill limber holes to suit, and fill again with epoxy same as for the engine mount bolts.
Yes transon vertical knees are also good, depends on what horsepower you are putting on the back. They can be placed right in the centre and/or two on either side of centre to suit your arrangement.

 

Thanks again for the guidance. I think I'm just about ready to make some sawdust. I'll admit I had to consult with Google to figure out what 'limber holes' were, but now I've got another term to add to my nautical vocabulary.
I'll try to get some pictures posted when there's some interesting progress.

 

First buy this book Runabout Renovation Easy to read. It is a bit old (Copyright 1992), but I don't think much has really changed since then. It will be the best $10-20 you will spend on your project !

There is an entire chapter on replacing a transom. It answers your questions specifically. Ther is another chapter on replacing a floor and stringers. I won't try to summarize what this knowledgeable, experienced author has written in 2 major chapters.

Personally, I would add another cradle about 1/3 to 1/2 forward from the stern. If you are going to pull out the stringer you may have to add 2 cradles and longitudinal bracing. You want zero flexing while you replace the stringers and floor.

 

Motorhead- Probably the best way to ensure the ply transom is snug against the glass is to drill a (hate the word) bunch of holes thru all the layers, and after you glue them all, you can "clamp" everything tight with screws. Just make sure that you wax the screws and washers so they come out fairly easy. Then one dry, you remove the bolts, clean the holes of any wax, and then fill the holes with thickened resin.

 

i was just looking at your pics,, and did a quick read,, and see that you braced across ya stern,,,but you should have cross bracing too. your board keeps it from spreading, but doesnt keep it from ricking off diagonally.

 

Hello, I'm in the final stages of a major transom repair on a 19' center console fishing skiff, and have over 3 grand invested, so I can appreciate the advice above. I removed the inner liner, sawcut out the inner transom skin, removed all the rotted plywood, then ran out of time and energy. I hired a fiberglass repair guy to complete the job, and gave him all the materials.

I eventually took the boat away from him because he was trying to scam at every opportunity, and am almost finished. I finished repairing the stringers, scarfing and tabbing into the transom, dropped the inner liner back on, joined the transom, and rescrewed the hull-deck joint.

I had the omc dealer re-mount my 140hp envirude outboard using their bolt jig. They siliconed the bolt holes.

Now while re-drilling the holes for the scupper drains and transom splash well drains, I found a gap (about 1/8")between the outer transom skin (about 3/8" frp) and the new plywood. The repair guy was supposed to bed the plywood with layers of mat and clamp thoroughly to prevent this. At least the new plywood had one layer of mat stuck to it to keep it dry.

I have been flowing slightly thinned epoxy into the crack (about 16 oz. already and the level is only about 8" high) and is taking forever. I need to inject more epoxy and am thinking about tapping some holes, connecting threaded barb fittings, connecting a hose and funnel to gravity feed/force in more resin. Any suggestions would be helpful.

Also I am wondering about the motor bolt holes, and if the gap exists there, I need to remove the motor, and fill the gap there also. My friend has a bobcat with forks and I can use it to lift my motor. Is there a special bracket to attach the flywheel to lift the motor, any suggestions for this?? Thanks folks, I will post some photos soon.

This has been a 3 year project, and I am dying to get it finished. The boat is looking good, I've replaced all rotten wood, dug out all wet foam & re-foamed, refinished the gas tank, re-plumbed all hoses, enlarged the scupper drains from 3/4" to 1-1/2", re-compartmented, moved the batteries into the center conole, added a live well under the leaning post, added a washdown pump.

I'm finally getting close to some minor gelcoat refinishing, then I can re-wire and run the motor controls, and get back out on the water!

I don't think I will take on a project like this again, but I have learned a lot about boat building, design, and appreciate good construction.

 

REPEAT First buy this book Runabout Renovation

If people followed the authors method of replacing a transom, there would be no voids.

His methods are proven (after many failures). His instructions are written in a simple, easy to understand way.

 

Thanks old wizard. I'ts a little late for the book reference at this stage of the game. I could probably write a book myself at this point with all the lessons I have learned.

Know anything about force feeding resin, and hoisting 140 hp outboards? Thanks again.

 

Skullhooker,

I understand your problem. Salvaging someone else's shoddy work sucx, but has to be done. This article http://www.rotdoctor.com/glass/GLrotrepair.html is based on an epoxy -based rot preventer, but the techniques on filling in transom gaps might help. Since you've found a gap and you know the work was poorly done, you really need to know if the gap exists over all the transom's surface. Drilling more holes sounds radical, but necessary. The good news is that if the gap is all across the transom, vertical holes will enable filling completely in one go. Otherwise, drilling holes wherever necessary and injecting as you mentioned would work. Since the layer of mat will prevent soaking the plywood, I think using some filler for strength would be better at this point.

 

First, you need a lifting ring. Don't screw around with straps, etc. Pay the $50 (or whatever) and order it from your dealer. Be careful, there are several different styles and you need the "right one" !

Most auto engine lifters (sometimes called cherry pickers) usually won't go high enough, but check around the rental shops and maybe you will find one !

The best I can think of is a cross beam (at least 2 - 2x8) supported by a couple of crossed 2x8 over the transom. You will probably have to do this out of the garage because the cross beam will have to be about 6' above the transom. Then You can hang a chain fall or come-along from the cross beam. You'll need some good side to side bracing as well.

Then using a rented engine lifter, you can get the engine upright and wheel it over to the cross beam and transfer it.

 

Thanks Charlie and Oldwizard, I have a lifting eye ordered, need to make a beefy "sawhorse" to hang the motor on while I finish the repair, and will mix some milled fibers with the epoxy to inject around the motor mounting area and holes. I have a fabricated aluminum top cap, and two transom bolt backing plates to help spread the load. Thanks again!

Any tips for building a motor stand? I can't tie up my friend's Bobcat for too long, and the epoxy will need to cure for a day or two before I can re-mount. The engine weighs about 360 lbs. according to the shop manual.